Japanese Patent Laid-Open Publication No. 2004-328965 discloses a technique for constructing a stator by using divided cores formed by sintering magnetic powder. Specifically, a stator is assembled by alternately arranging trapezoidal divided cores.
Japanese Patent Laid-Open Publication No. 2003-224940 discloses a technique for constructing a stator by engaging a concave part of a tooth with a convex part provided on the inner peripheral surface of a ring-shaped core back. In this technique, at least either one of the core back and the tooth is formed of magnetic powder.
Japanese Patent Laid-Open Publication No. 2005-39992 discloses a technique for constructing a stator by combining a plurality of divided cores each having a tooth. In this technique, an arcuate concave part is provided on one side surface of the divided core, and an arcuate convex part is provided on the other side surface thereof, by which the adjacent divided cores are engaged with each other to receive an external force over a large-area surface, and thereby preventing stress concentration. Each of the divided cores is made by building up laminate materials.
Japanese Patent Laid-Open Publication No. Hei11-275830 discloses a technique for fixing a lapped part of the adjacent divided cores to a frame with bolts. In this technique, surfaces serving as paths of magnetic flux are securely brought into contact with each other to allow the magnetic flux to pass therethrough easily.
Japanese Patent Laid-Open Publication No. Hei11-127549 describes a technique for fixing a stator by engaging a plurality of teeth with a cylindrical core back.
A powder magnetic core has insufficient strength against high stress, because the use of a low-loss material decreases the strength. However, the aforementioned patent documents do not disclose a technique for decreasing stress acting on the powder magnetic core.